1. Field of the Invention
The field of the invention includes methods of measuring and recording the maximum pressure attained in a fluid, particularly fluids in which the inaccessibility and the small size of the volume under test has made the use of standard pressure transducers difficult.
2. Description of the Prior Art
It is often desirable to measure the pressure or compressive stress to which a fluid has been subjected. Detecting pressure changes is commonly done through the use of pressure transducers. These pressure transducers are usually electrical in nature and take the form of strain gages, moving-contact resistance element, or inductance, reluctance, capacitative or piezo electric devices. Standard pressure transducers are accurate and generally satisfactory.
These transducers do have at least two shortcomings. First, they require a minimum volume in which to operate. In most cases, about 0.1 cubic centimeter is necessary to accommodate even the smallest transducer. A second shortcoming is the need for electrical connections to be routed to and from the volume to be measured. In some cases, providing the necessary electrical leads with access to the volume to be measured is difficult, other shortcomings include selecting a measuring technique which is inert, inexpensive and effective over a wide range of pressures.
Both of these shortcomings were evident during testing to determine the cause of a failure of a solid rocket motor (SRM). As shown in FIG. 1a, the SRM is composed of segments 1, and one series of tests examined pressures exerted during the stacking of the segments. Particular interest was directed to the maximum pressure exerted on grease 3 from the o-ring 5 trapped in the region as indicated in FIG. 1b. Concern had been raised that a high pressure in this region could initiate a separation between the case insulation 7 and either the upper segment case 9 or the lower segment case 11. The small size of this region and the requirement that no holes were allowed to be drilled through the lower segment case 11 made the implementation of standard pressure transducers difficult.
One object of the present invention is the use of a method of measuring pressure which is useful in small, constricted areas which are not suited to the use of standard pressure transducers. Another object of the invention is to use a technique which is relatively inert so as not to affect the chemical properties of the substancing being measured. Yet another object of the invention is to develop a method of measuring pressure across a wide range, i.e., from less than 50 psi to over 1000 psi. Still another object of the invention is to develop a method of measuring pressure that is inexpensive, and non-destructive and reliable.